Enhanced glucose availability for working muscles reduces exercise hyperthermia in dogs

Area of Science:

• Exercise Physiology
• Animal Metabolism
• Thermoregulation

Background:

• Exercise increases body temperature and metabolic rate.
• Fuel utilization impacts physiological responses during physical activity.
• Understanding thermoregulation is crucial for exercise performance and health.

Purpose of the Study:

• To investigate the effects of enhanced glucose availability on exercise responses in dogs.
• To compare metabolic and thermoregulatory differences between glucose infusion, elevated free fatty acid (FFA) levels, and control conditions.
• To determine the impact of carbohydrate utilization on exercise-induced hyperthermia and thermoregulatory efficiency.

Main Methods:

• Treadmill exercise protocol for 2 hours in dogs.
• Intravenous glucose infusion (25-30 mg.kg-1 X min-1).
• Induction of elevated plasma FFA concentrations (soya bean oil + heparin).
• Control experiments involving 24-hour fasting.
• Measurement of rectal and muscle temperatures, oxygen uptake (VO2), respiratory exchange ratio, and cardiac frequency.

Main Results:

• Enhanced glucose availability significantly reduced exercise-induced increases in rectal and muscle temperatures (by ~0.9°C).
• Glucose infusion led to a 16% lower oxygen uptake and an elevated respiratory exchange ratio compared to controls.
• Dogs with elevated plasma FFA showed a tendency towards increased body temperature responses during exercise.
• Thermoregulatory efficiency was significantly higher in dogs infused with glucose (0.962) compared to controls (0.947) and those with elevated FFA (0.931).

Conclusions:

• Increased carbohydrate contribution to energy yield during exercise markedly attenuates hyperthermia in dogs.
• This attenuation is associated with a reduced metabolic rate and improved thermoregulatory efficiency.
• Fuel substrate availability significantly influences physiological adaptations to exercise stress.